Low latency ack/nack transmission

ABSTRACT

Some embodiments of the present disclosure provide a user equipment (UE) having active device components and passive device components. Responsive to receiving downlink (DL) transmissions in time division duplexing (TDD) mode, the active device components perform DL decoding while the passive device components perform passive transmission of ACK/NACK data. Such passive transmission may involve encoding the ACK/NACK data in an altered version of received radio frequency (RF) signals and using so-called backscatter communications to reflect the received RF signals, with alteration, using the same frequency resources used to receive the DL transmissions.

TECHNICAL FIELD

The present disclosure relates generally to acknowledgement transmissionand, in particular embodiments, to reducing latency in suchtransmission.

BACKGROUND

Typical wireless communication devices are half duplex communicationdevices. Half duplex communication refers to an ability to either onlyreceive or only transmit using a given resource (such as a time slot ora particular frequency). That is, the device is not able to both receiveand transmit using the given resource. Examples of half duplexcommunication schemes include time division duplexing (TDD) andfrequency division duplexing (FDD). In TDD, once a communication devicereceives and decodes a downlink (DL) transmission, the communicationdevice then has to switch its transceiver from a DL mode to an up link(UL) mode in order to transmit an acknowledgement (ACK) or negativeacknowledgement (NACK) signal in response to the DL transmission.Switching from DL to UL (or vice versa) typically incurs a length oftime that may be referred to as latency. Communication protocols oftenaccount for the latency ahead of time by planning a length of time knownas a guard interval (GI).

For some types of communications, it is desirable to reduce the latencyof the ACK/NACK as much as possible. Half duplex communication, and TDDin particular, presents challenges to reducing ACK/NACK latency. If, forexample, the DL transmission consists of bursts of transport blocks(TBs), then the latency corresponding to the GIs, in addition to the ULresources required for ACK/NACK transmission, will add up, creating asignificant bottleneck for low-latency transmission.

Conventional solutions for reducing ACK/NACK latency may be shown tocreate other problems. FDD communication dedicates additional frequencyresources for ACK/NACK transmissions. This dedication reduces thespectrum efficiency of the overall communications system. Full-duplexcommunication requires complex hardware and increased power consumption.While this may be feasible for network equipment, a full duplextransceiver is impractical for mobile device implementation.

SUMMARY

Aspects of the present application provide a user equipment (UE) havingactive device components and passive device components. Responsive toreceiving downlink (DL) transmissions (e.g., bursty DL transmissions) intime division duplexing (TDD) mode, the active device components performDL decoding while the passive device components perform passivetransmission of ACK/NACK data. Such passive transmission may involveencoding the ACK/NACK data in an altered version of received radiofrequency (RF) signals corresponding to the DL transmissions and usingso-called backscatter communications to reflect the received RF signals,with alteration, using the same frequency resources used to receive theDL transmissions.

Since the ACK/NACK data is encoded in an altered version of an RFsignal, a reflection of the RF signal, with the encoded ACK/NACK data,can be received at a transmission point while the RF signal is beingtransmitted by the transmission point. Accordingly, any need for a guardinterval is obviated and, accordingly, latency is reduced. Furthermore,additional resources specifically assigned to transmission of ACK/NACKdata are not required because the same frequency resources are used toreflect, with alteration, the received RF signals and to receive the DLtransmissions.

According to an aspect of the present disclosure, there is provided amethod for an apparatus to reduce ACK/NACK transmission latency. Themethod includes receiving, by the apparatus, a first (RF) signalcomprising a first transport block, attempting, by the apparatus, todemodulate and decode the first transport block from the first RFsignal, receiving, by the apparatus, a second RF signal after the firstRF signal and reflecting, by the apparatus, the second RF signal whilealtering the second RF signal, the altered and reflected second RFsignal comprising a first feedback indicative of whether the firsttransport block was correctly or incorrectly demodulated and decoded bythe apparatus. Additionally, aspects of the present application providean apparatus for carrying out this method.

According to another aspect of the present disclosure, there is provideda method, at an apparatus, of receiving acknowledgement (ACK) ornegative acknowledgement (NACK) transmissions. The method includestransmitting, by the apparatus, a first radio frequency (RF) signalcomprising a first transport block, transmitting, by the apparatus, asecond RF signal after the first RF signal and receiving, by theapparatus, an altered and reflected version of the second RF signalincluding a first feedback indicative of whether the first transportblock was correctly or incorrectly demodulated and decoded.Additionally, aspects of the present application provide an apparatusfor carrying out this method.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present embodiments, and theadvantages thereof, reference is now made, by way of example, to thefollowing descriptions taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a schematic diagram of a communication system in whichembodiments of the disclosure may occur, the communication systemincludes an example user equipment and an example base station;

FIG. 2 illustrates, as a block diagram, the example user equipment ofFIG. 1, according to aspects of the present disclosure;

FIG. 3 illustrates, as a block diagram, the example base station of FIG.1, according to aspects of the present disclosure;

FIG. 4 illustrates a summary of user equipment and base stationoperations in a context of structure and timing of transport blocks,according to aspects of the present disclosure;

FIG. 5 illustrates a flow diagram of communication between the basestation and the user equipment, according to aspects of the presentdisclosure; and

FIG. 6 illustrates example steps in a method of operating the userequipment in the context of reflecting RF signals encoded with ACK/NACKdata, according to aspects of the present disclosure.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

For illustrative purposes, specific example embodiments will now beexplained in greater detail in conjunction with the figures.

The embodiments set forth herein represent information sufficient topractice the claimed subject matter and illustrate ways of practicingsuch subject matter. Upon reading the following description in light ofthe accompanying figures, those of skill in the art will understand theconcepts of the claimed subject matter and will recognize applicationsof these concepts not particularly addressed herein. It should beunderstood that these concepts and applications fall within the scope ofthe disclosure and the accompanying claims.

Moreover, it will be appreciated that any module, component, or devicedisclosed herein that executes instructions may include, or otherwisehave access to, a non-transitory computer/processor readable storagemedium or media for storage of information, such as computer/processorreadable instructions, data structures, program modules and/or otherdata. A non-exhaustive list of examples of non-transitorycomputer/processor readable storage media includes magnetic cassettes,magnetic tape, magnetic disk storage or other magnetic storage devices,optical disks such as compact disc read-only memory (CD-ROM), digitalvideo discs or digital versatile discs (i.e., DVDs), Blu-ray Disc™, orother optical storage, volatile and non-volatile, removable andnon-removable media implemented in any method or technology,random-access memory (RAM), read-only memory (ROM), electricallyerasable programmable read-only memory (EEPROM), flash memory or othermemory technology. Any such non-transitory computer/processor storagemedia may be part of a device or accessible or connectable thereto.Computer/processor readable/executable instructions to implement anapplication or module described herein may be stored or otherwise heldby such non-transitory computer/processor readable storage media.

FIGS. 1, 2 and 3 illustrate examples of networks and devices that couldimplement any or all aspects of the present disclosure.

FIG. 1 illustrates an example communication system 100. In general, thesystem 100 enables multiple wireless or wired elements to communicatedata and other content. The purpose of the system 100 may be to providecontent (voice, data, video, text) via broadcast, narrowcast, userdevice to user device, etc. The system 100 may operate efficiently bysharing resources, such as bandwidth.

In this example, the communication system 100 includes a firstelectronic device (ED) 110A, a second ED 1106 and a third ED 110C(individually or collectively 110), a first radio access network (RAN)120A and a second RAN 120B (individually or collectively 120), a corenetwork 130, a public switched telephone network (PSTN) 140, theInternet 150 and other networks 160. Although certain numbers of thesecomponents or elements are shown in FIG. 1, any reasonable number ofthese components or elements may be included in the communication system100.

The EDs 110 are configured to operate, communicate, or both, in thecommunication system 100. For example, the EDs 110 are configured totransmit, receive, or both via wireless communication channels. Each ED110 represents any suitable end user device for wireless operation andmay include such devices (or may be referred to) as a userequipment/device (UE), wireless transmit/receive unit (WTRU), mobilestation, mobile subscriber unit, cellular telephone, station (STA),machine type communication device (MTC), Internet of Things (IoT)device, personal digital assistant (PDA), smartphone, laptop, computer,touchpad, wireless sensor, or consumer electronics device.

In FIG. 1, the first RAN 120A includes a first base station 170A and thesecond RAN includes a second base station 170B (individually orcollectively 170). Each base station 170 is configured to wirelesslyinterface with one or more of the EDs 110 to enable access to any otherbase station 170, the core network 130, the PSTN 140, the internet 150and/or the other networks 160. For example, the base stations 170 mayinclude (or be) one or more of several well-known devices, such as abase transceiver station (BTS), a Node-B (NodeB), an evolved NodeB(eNodeB), a Home eNodeB, a gNodeB, a transmission and receive point(TRP), a site controller, an access point (AP) or a wireless router. AnyED 110 may be alternatively or additionally be configured to interface,access or communicate with any other base station 170, the internet 150,the core network 130, the PSTN 140, the other networks 160 or anycombination of the preceding. The communication system 100 may includeRANs, such as the RAN 120B, wherein the corresponding base station 170Baccesses the core network 130 via the internet 150, as shown.

The EDs 110 and the base stations 170 are examples of communicationequipment that can be configured to implement some or all of thefunctionality and/or embodiments described herein. In the embodimentshown in FIG. 1, the first base station 170A forms part of the first RAN120A, which may include other base stations (not shown), base stationcontroller(s) (BSC, not shown), radio network controller(s) (RNC, notshown), relay nodes (not shown), elements (not shown) and/or devices(not shown). Any base station 170 may be a single element, as shown, ormultiple elements, distributed in the corresponding RAN 120, orotherwise. Also, the second base station 170B forms part of the secondRAN 120B, which may include other base stations, elements and/ordevices. Each base station 170 transmits and/or receives wirelesssignals within a particular geographic region or area, sometimesreferred to as a “cell” or “coverage area.” A cell may be furtherdivided into cell sectors and a base station 170 may, for example,employ multiple transceivers to provide service to multiple sectors. Insome embodiments, there may be established pico or femto cells where theradio access technology supports such. In some embodiments, multipletransceivers could be used for each cell, for example usingmultiple-input multiple-output (MIMO) technology. The number of RANs 120shown is exemplary only. Any number of RANs may be contemplated whendevising the communication system 100.

The base stations 170 communicate with one or more of the EDs 110 overone or more air interfaces 190 using wireless communication links, e.g.,radio frequency (RF) wireless communication links, microwave wirelesscommunication links, infrared (IR) wireless communication links, visiblelight (VL) communications links, etc. The air interfaces 190 may utilizeany suitable radio access technology. For example, the communicationsystem 100 may implement one or more orthogonal or non-orthogonalchannel access methods, such as code division multiple access (CDMA),time division multiple access (TDMA), space division multiple access(SDMA), frequency division multiple access (FDMA), orthogonal FDMA(OFDMA) or single-carrier FDMA (SC-FDMA) in the air interfaces 190.

A base station 170 may implement Universal Mobile TelecommunicationSystem (UMTS) Terrestrial Radio Access (UTRA) to establish the airinterface 190 using wideband CDMA (WCDMA). In doing so, the base station170 may implement protocols such as High Speed Packet Access (HSPA),Evolved HPSA (HSPA+) optionally including High Speed Downlink PacketAccess (HSDPA), High Speed Packet Uplink Access (HSUPA) or both.Alternatively, a base station 170 may establish the air interface 190with Evolved UTMS Terrestrial Radio Access (E-UTRA) using LTE, LTE-A,LTE-B and/or 5G New Radio (NR). It is contemplated that thecommunication system 100 may use multiple channel access functionality,including such schemes as described above. Other radio technologies forimplementing air interfaces include IEEE 802.11, 802.15, 802.16,CDMA2000, CDMA2000 1x, CDMA2000 EV-DO, IS-2000, IS-95, IS-856, GSM, EDGEand GERAN. Of course, other multiple access schemes and wirelessprotocols may be utilized.

The RANs 120 are in communication with the core network 130 to providethe EDs 110 with various services such as voice communication services,data communication services and other communication services. The RANs120 and/or the core network 130 may be in direct or indirectcommunication with one or more other RANs (not shown), which may or maynot be directly served by the core network 130 and may or may not employthe same radio access technology as the first RAN 120A, the second RAN120B or both. The core network 130 may also serve as a gateway accessbetween (i) the RANs 120 or EDs 110 or both, and (ii) other networks(such as the PSTN 140, the Internet 150 and the other networks 160).

The EDs 110 may communicate with one another over one or more sidelink(SL) air interfaces 180 using wireless communication links, e.g., radiofrequency (RF) wireless communication links, microwave wirelesscommunication links, infrared (IR) wireless communication links, visiblelight (VL) communications links, etc. The SL air interfaces 180 mayutilize any suitable radio access technology and may be substantiallysimilar to the air interfaces 190 over which the EDs 110 communicationwith one or more of the base stations 170 or they may be substantiallydifferent. For example, the communication system 100 may implement oneor more channel access methods, such as CDMA, TDMA, FDMA, SDMA, OFDMA orSC-FDMA in the SL air interfaces 180. In some embodiments, the SL airinterfaces 180 may be, at least in part, implemented over unlicensedspectrum.

Some or all of the EDs 110 may include functionality for communicatingwith different wireless networks over different wireless links usingdifferent wireless technologies and/or protocols. Instead of wirelesscommunication (or in addition thereto), the EDs 110 may communicate viawired communication channels to a service provider or a switch (notshown) and to the Internet 150. The PSTN 140 may include circuitswitched telephone networks for providing plain old telephone service(POTS). The Internet 150 may include a network of computers and subnets(intranets) or both and incorporate protocols, such as internet protocol(IP), transmission control protocol (TCP) and user datagram protocol(UDP). The EDs 110 may be multimode devices capable of operationaccording to multiple radio access technologies and incorporate multipletransceivers necessary to support multiple radio access technologies.

FIG. 2 illustrates example components that may implement the methods andteachings according to the present disclosure. In particular, FIG. 2illustrates an example UE 110. These components could be used in thecommunication system 100 or in any other suitable system.

As shown in FIG. 2, the UE 110 includes at least one processor orprocessing unit 200. The processing unit 200 implements variousprocessing operations of the UE 110. For example, the processing unit200 could perform signal coding, bit scrambling, data processing, powercontrol, input/output processing, or any other functionality, therebyenabling the UE 110 to operate in the communication system 100. Theprocessing unit 200 may also be configured to implement some or all ofthe functionality and/or embodiments described in more detail herein.Each processing unit 200 includes any suitable processing or computingdevice configured to perform one or more operations. Each processingunit 200 could, for example, include a microprocessor, amicrocontroller, a digital signal processor, a field programmable gatearray or an application specific integrated circuit.

The UE 110 also includes at least one transceiver 202. The transceiver202 includes an RF circuit 210 that is configured to modulate data orother content for transmission by at least one antenna 204. Thetransceiver 202 is also configured to demodulate data or other contentreceived by the at least one antenna 204. Each transceiver 202 includesany suitable structure for generating signals for wireless or wiredtransmission and/or processing signals received wirelessly or by wire.Each antenna among the at least one antenna 204 includes any suitablestructure for transmitting and/or receiving wireless or wired signals.One or multiple transceivers 202 could be used in the UE 110. One ormultiple antennas 204 could be used in the UE 110. Although shown as asingle functional unit, a transceiver 202 could also be implementedusing at least one transmitter and at least one separate receiver.

The RF circuit 210 is illustrated as including a set of active devicecomponents 211 connected to one of the antennas 204. In addition, the RFcircuit 210 is illustrated as including a set of passive devicecomponents 212 connected to an associated one of the antennas 204.

The term “passive,” as used herein in the phrase “passive devicecomponents,” bears clarification. In a typical discussion of electroniccomponents, the term “passive” is given to those electronic componentsthat lack an ability to control electric current by means of anotherelectrical signal. Examples of passive electronic components arecapacitors, resistors, inductors, transformers and some diodes. Incontrast, the term “active” is given to those electronic components thatcan control the flow of electricity by means of another electricalsignal. Some examples of active electronic components are transistors,vacuum tubes and silicon-controlled rectifiers.

In a discussion of electronic components in the present application, theterm “passive” is given to those electronic components that lack arequirement for conversion to baseband when receiving or transmittingsignals. In contrast, the term “active” is given to those electroniccomponents that employ conversion to baseband when receiving ortransmitting. In other words, the “passive” circuits of the presentapplication may, in some examples, consist of only those electroniccomponents that lack an ability to control electric current by means ofanother electrical signal, and in some other examples, may furthercomprise those electronic components that can control the flow ofelectricity by means of another electrical signal. Conveniently, passivedevice components 212 are configured to perform their functions in theRF domain in contrast to the active device components 211, which areconfigured to perform their functions in the baseband domain. As aconsequence, the power consumption level of the passive devicecomponents 212 is very low relative to the power consumption level ofthe active device components 211.

In accordance with aspects of the present application, the processingunit 200 of the electronic device 110 may cause the passive devicecomponents 212 to perform certain functions known to be performed by theactive device components 211, thereby reducing overall powerconsumption. Indeed, the amount by which the overall power consumptionis expected to be reduced is roughly the power consumption associatedwith the active device components 211 performing the certain functions.

The UE 110 further includes one or more input/output devices 206 orinterfaces (such as a wired interface to the Internet 150). Theinput/output devices 206 permit interaction with a user or other devicesin the network. Each input/output device 206 includes any suitablestructure for providing information to, or receiving information from, auser, such as a speaker, a microphone, a keypad, a keyboard, a displayor a touch screen, including network interface communications.

In addition, the UE 110 includes at least one memory 208. The memory 208stores instructions and data used, generated or collected by the UE 110.For example, the memory 208 could store software instructions or modulesconfigured to implement some or all of the functionality and/orembodiments described herein and that are executed by the processingunit 200. Each memory 208 includes any suitable volatile and/ornon-volatile storage and retrieval device. Any suitable type of memorymay be used, such as a random access memory (RAM), a read only memory(ROM), a hard disk, an optical disc, a subscriber identity module (SIM)card, a memory stick, a secure digital (SD) memory card and the like.

As illustrated in FIG. 3, the base station 170 includes at least oneprocessing unit 350, at least one transmitter 352, at least one receiver354, one or more antennas 356, at least one memory 358 and one or moreinput/output devices or interfaces 366. A transceiver (not shown) may beused instead of the transmitter 352 and receiver 354. A scheduler 353may be coupled to the processing unit 350. The scheduler 353 may beincluded within, or operated separately from, the base station 170. Theprocessing unit 350 implements various processing operations of the basestation 170, such as signal coding, bit scrambling, data processing,power control, input/output processing or any other functionality. Theprocessing unit 350 can also be configured to implement some or all ofthe functionality and/or embodiments described in more detail above.Each processing unit 350 includes any suitable processing or computingdevice configured to perform one or more operations. Each processingunit 350 could, for example, include a microprocessor, amicrocontroller, a digital signal processor, a field programmable gatearray or an application specific integrated circuit.

Each transmitter 352 includes any suitable structure for generatingsignals for wireless or wired transmission to one or more EDs 110 orother devices. Each receiver 354 includes any suitable structure forprocessing signals received wirelessly or by wire from one or more EDs110 or other devices. Although shown as separate components, at leastone transmitter 352 and at least one receiver 354 could be combined intoa transceiver. Each antenna 356 includes any suitable structure fortransmitting and/or receiving wireless or wired signals. Although acommon antenna 356 is shown here as being coupled to both thetransmitter 352 and the receiver 354, one or more antennas 356 could becoupled to the transmitter 352 and one or more separate antennas 356could be coupled to the receiver 354. Each memory 358 includes anysuitable volatile and/or non-volatile storage and retrieval device(s)such as those described above in connection to the UE 110. The memory358 stores instructions and data used, generated or collected by thebase station 170. For example, the memory 358 could store softwareinstructions or modules configured to implement some or all of thefunctionality and/or embodiments described above and that are executedby the processing unit 350.

Each input/output device 366 permits interaction with a user or otherdevices in the network. Each input/output device 366 includes anysuitable structure for providing information to or receiving/providinginformation from a user, including network interface communications.

Additional details regarding the UE 110 and the base stations 170 areknown to those of skill in the art. As such, these details are omittedhere for clarity.

It may be considered desirable to reduce the latency of ACK/NACK datatransmissions responsive to DL transmissions, especially bursty DLtransmissions.

According to aspects of the present application, responsive toreceiving, at the UE 110, DL transmissions such as bursty DLtransmissions, the active device components 211 perform DL decodingwhile the passive device components 210 performs passive reflection in amanner that allows transmission of ACK/NACK data. Such passivereflection may involve encoding the ACK/NACK data in an altered versionof received RF signals corresponding to the DL transmissions and usingso-called backscatter communications to reflect the altered version ofthe received RF signal.

Using the proposed solution, ACK/NACK data latency is reduced due to anabsence of GIs. Indeed, no GI is necessary, since the UE 110 need nottransit to a UL transmission mode. Since the passive reflection, by thenature of reflection, uses the same frequency resources used to receivethe DL transmissions, specific UL ACK/NACK frequency resources areunnecessary.

It is expected herein that there exists full-duplex (FD) capability atthe base station 170. Notably, at the base station 170, the ACK/NACKdata can be decoded from the altered version of the RF signalscorresponding to the DL transmissions, since the base station 170 knowsthe contents of the DL transmissions.

One use case for aspects of the present application may be found insmart factories, where there is typically a short distance between TPand UE to enable backscatter communications and low latency transmissionis beneficial.

FIG. 4 illustrates a summary of UE and BS operations in a context ofstructure and timing of transport blocks. FIG. 5 illustrates a flowdiagram of communication between the BS 170 and the UE 110. FIG. 6illustrates example steps in a method of operating the UE 110 in thecontext of UL ACK/NACK passive reflection.

In a first time slot 402-1, the transmitter 352 of the BS 170 transmits(step 502) a first RF signal 412-1 of a DL transmission.

The TB carried by the first RF signal 412-1 includes a plurality ofsymbols (not specifically shown). The first symbol or symbols of thefirst TB may implement a physical downlink control channel (PDCCH)signaling that allows the BS 170 to instruct the UE 110 to enable ULACK/NACK reflection. There are, of course, other types of controlsignaling by which the BS 170 can instruct the UE 110 to enable ULACK/NACK reflection. The other types of control signaling include RadioResource Control (RRC) signaling and signaling that uses Media AccessControl (MAC) Control Elements (CEs).

Responsive to receiving (step 504) the first RF signal 412-1implementing the PDCCH signaling, the active device components 211enable the passive device components 210. Responsive to receiving (step601) an enable instruction, the passive device components 210 perform a“mirror reflection” operation. In a “mirror reflection” operation, thepassive device components 210 use backscatter communications to reflect(step 506) a mirror RF signal 430 that is an unaltered version of thefirst RF signal 412-1. In a manner that beneficially conservesresources, it is the nature of the passive device components 210reflecting (step 506) the unaltered version of the first RF signal asthe mirror RF signal 430 that the same frequency resources are used bythe active device components 211 to receive (step 504) the first RFsignal 412-1.

The active device components 211 of the UE 110, upon receiving (step504) the first RF signal 412-1 in the first time slot 402-1, demodulateand decode (step 612) the first RF signal 412-1 to yield a first decodedTB 422-1. The active device components 211 generate (step 614) ACK/NACKfeedback data based on the first decoded TB 422-1. The active devicecomponents 211 also provide, to the passive device components 210, theACK/NACK feedback data, which is understood to be related to the firstdecoded TB 422-1.

Responsive to receiving the ACK/NACK feedback data, the passive devicecomponents 210 of the UE 110 select (step 616), on the basis of theACK/NACK feedback data specific to the first decoded TB 422-1 receivedfrom the active device components 211, an ACK/NACK codeword vector froma pre-configured ACK/NACK codebook. Each ACK/NACK codeword vector in thepre-configured ACK/NACK codebook includes a plurality of complexsymbols.

The pre-configured ACK/NACK codebook may be stored in the memory 208 ofthe UE 110 after having been received from the BS 170 (or other devicein the network 100) at some earlier point in time. In aspects of thepresent application, the pre-configured ACK/NACK codebook may beprovided by the BS 170 to the UE 110 using RRC signaling or signalingthat uses MAC-CEs. Alternatively, the pre-configured ACK/NACK codebookmay be provided by the BS 170 to the UE 110 using PDCCH signaling.

Still in the first time slot 402-1, upon receiving (step 508) the mirrorRF signal 430, the receiver 354 of the BS 170 may perform analysis onthe received reflected signal, thereby resulting in a channel and rangeestimate 440.

In a second time slot 402-2, the transmitter 352 of the BS 170 transmits(step 510) a second RF signal 412-2 and the passive device components210 of the UE 110 reflect (step 514) the second RF signal 412-2 as thefirst ACK/NACK RF signal 432-1. While reflecting (step 514) the secondRF signal 412-2, the passive device components 210 alter the second RFsignal 412-2, employing the selected ACK/NACK codeword vector, to arriveat the first ACK/NACK RF signal 432-1. In a manner that beneficiallyconserves resources, the passive device components 210 reflect (step514) the second RF signal 412-2 using the same frequency resources asare used by the active device components 211 to receive (step 512) thesecond RF signal 412-2.

The active device components 211 of the UE 110, upon receiving (step512) the second RF signal 412-2 in the second time slot 402-2,demodulate and decode (step 622) the second RF signal 412-2 to yield asecond decoded TB 422-2. The active device components 211 generate (step624) ACK/NACK feedback data based on the second decoded TB 422-2. Theactive device components 211 also provide, to the passive devicecomponents 210, the ACK/NACK feedback data, which is understood to berelated to the second decoded TB 422-2.

Responsive to receiving the ACK/NACK feedback data, the passive devicecomponents 210 of the UE 110 select (step 626), on the basis of theACK/NACK feedback data specific to the second decoded TB 422-2 receivedfrom the active device components 211, an ACK/NACK codeword vector fromthe pre-configured ACK/NACK codebook.

Still in the second time slot 402-2, the receiver 354 of the BS 170receives the first ACK/NACK RF signal 432-1 and decodes the firstACK/NACK RF signal 432-1. The result of decoding the first ACK/NACK RFsignal 432-1 is first decoded ACK/NACK data 442-1, which is feedbackindicative of whether the first decoded TB 422-1 was correctly orincorrectly decoded.

In a third time slot 402-3, the transmitter 352 of the BS 170 transmits(step 518) a third RF signal 412-3 and the passive device components 210of the UE 110 reflect (step 522) the third RF signal as the secondACK/NACK RF signal 432-2. While reflecting (step 522) the third RFsignal 412-3, the passive device components 210 alter the third RFsignal 412-3, employing the selected ACK/NACK codeword vector, to arriveat the second ACK/NACK RF signal 432-2. In a manner that beneficiallyconserves resources, the passive device components 210 reflect (step522) the third RF signal 412-3 using the same frequency resources as areused by the active device components 211 to receive (step 520) the thirdRF signal 412-3.

The active device components 211 of the UE 110, upon receiving (step520) the third RF signal 412-3 in the third time slot 402-3, demodulateand decode the third RF signal 412-3 to yield a third decoded TB 422-3.The active device components 211 generate ACK/NACK feedback data basedon the third decoded TB 422-3. The active device components 211 alsoprovide, to the passive device components 210, the ACK/NACK feedbackdata specific to the third decoded TB 422-3.

The BS 170 may transmit, as part of the third RF signal 412-3, somePDCCH signaling that reports a decoding status for the first ACK/NACKsignal 432-1. There are, of course, other types of control signaling bywhich the BS 170 can report a decoding status to the UE 110.

Responsive to receiving the ACK/NACK feedback data, the passive devicecomponents 210 of the UE 110 select, on the basis of the ACK/NACKfeedback data specific to the third decoded TB 422-3 received from theactive device components 211, an ACK/NACK codeword vector from thepre-configured ACK/NACK codebook.

Still in the third time slot 402-3, the receiver 354 of the BS 170receives the second ACK/NACK RF signal 432-2 and decodes the secondACK/NACK RF signal 432-2. The result of decoding the second ACK/NACK RFsignal 432-2 is second decoded ACK/NACK data 442-2, which is feedbackindicative of whether the second decoded TB 422-2 was correctly orincorrectly decoded.

In a fourth time slot 402-4, the transmitter 352 of the BS 170 transmitsa fourth RF signal 412-4 and the passive device components 210 of the UE110 reflect the fourth RF signal 412-4 as the third ACK/NACK RF signal432-3. While reflecting the fourth RF signal 412-4, the passive devicecomponents 210 alter the fourth RF signal 412-4, employing the selectedACK/NACK codeword vector, to arrive at the third ACK/NACK RF signal432-3. In a manner that beneficially conserves resources, the passivedevice components 210 reflect the fourth RF signal 412-4 using the samefrequency resources as are used by the active device components 211 toreceive the fourth RF signal 412-4.

The active device components 211 of the UE 110, upon receiving thefourth RF signal 412-4 in the fourth time slot 402-4, demodulate anddecode the fourth RF signal 412-4 to yield a fourth decoded TB 422-4.The active device components 211 generate ACK/NACK feedback data basedon the fourth decoded TB 422-4. The active device components 211 alsoprovide, to the passive device components 210, the ACK/NACK feedbackdata specific to the fourth decoded TB 422-4.

The BS 170 may transmit, as part of the fourth RF signal 412-4, somePDCCH signaling that reports a decoding status for the second ACK/NACKTB 432-2. There are, of course, other types of control signaling bywhich the BS 170 can report a decoding status to the UE 110.

Responsive to receiving the ACK/NACK feedback data, the passive devicecomponents 210 of the UE 110 select, on the basis of the ACK/NACKfeedback data specific to the fourth decoded TB 422-4 received from theactive device components 211, an ACK/NACK codeword vector from thepre-configured ACK/NACK codebook.

Still in the fourth time slot 402-4, the receiver 354 of the BS 170receives the third ACK/NACK RF signal 432-3 and decodes the thirdACK/NACK RF signal 432-3. The result of decoding the third ACK/NACK RFsignal 432-3 is third decoded ACK/NACK data 442-3, which is feedbackindicative of whether the third decoded TB 422-3 was correctly orincorrectly decoded. While only four time slots have been illustrated inthis particular example, the method may continue in similar fashion overfurther time slots.

For simplicity of illustration, the mirror RF signal 430 is illustratedas aligned with the first time slot 402-1. Similarly, the first ACK/NACKRF signal 432-1 is illustrated as aligned with the second time slot402-2, the second ACK/NACK RF signal 432-2 is illustrated as alignedwith the third time slot 402-3 and the third ACK/NACK RF signal 432-3 isillustrated as aligned with the fourth time slot 402-4. Collectively,the act of reflecting that has been described hereinbefore as leading tothe mirror RF signal 430, the first ACK/NACK RF signal 432-1, the secondACK/NACK RF signal 432-2 and the third ACK/NACK RF signal 432-3 may bereferenced as “backscatter communications.” It should be clear thatthere may be a time offset between the temporal boundaries of the timeslots 402 and the commencement of the reflecting. Indeed, the UE 110 maybe instructed, by the BS 170, to wait an initial time offset, from thebeginning of the respective time slot 402, before commencing reflecting.The initial time offset before commencing reflecting can be configuredto be TB-specific, i.e., the timing offset for the commencement ofreflecting employing an ACK/NACK codeword vector that has been selectedon the basis of ACK/NACK feedback data generated from decoded TB 422-imay be different than commencement of reflecting employing an ACK/NACKcodeword vector that has been selected on the basis of ACK/NACK feedbackdata generated from TB 422-k. In some embodiments, the timing offsetconfiguration of TBs can be signaled from the BS 170 to the UE 110through higher layer signaling including RRC and MAC-CE.

The ACK/NACK feedback data may be implemented as a single decodingstatus indicator bit indicative of a decoding status for a correspondingdecoded TB 422. The ACK/NACK feedback data may include a plurality ofdecoding status indicator bits, with each decoding status indicator bitin the plurality of bits indicative of a decoding status for acorresponding decoded TB 422. In some embodiments, the ACK/NACK feedbackdata may include a decoding status indicator bit corresponding to eachcode block among a plurality of code blocks included in a decoded TB422. The ACK/NACK feedback data may include an index to a specific TB.The ACK/NACK feedback data may include an index to a specific code blockindex inside a TB. The ACK/NACK feedback data may include a combinationof indices to specific TBs and specific code blocks. In some aspects ofthe present application, the ACK/NACK feedback data may include bitsindicative of a decoding status for more than one TB transmitted in thepast.

As discussed in view of FIG. 4, the BS 170 receives, from the UE 110, anACK/NACK RF signal 432 for every RF signal 412 transmitted by the BS170. It is the task of the BS 170 to decode the ACK/NACK feedback datathat has been included, by the UE 110, in each ACK/NACK RF signal 432.

It has been discussed hereinbefore that the altering of a given RFsignal 412 is performed on the basis of ACK/NACK feedback data, specificto the TB that is decoded from the RF signal 412, received from theactive device components 211 and the pre-configured ACK/NACK codebook.More specifically, the passive device components 210 of the UE 110select an ACK/NACK codeword vector from the pre-configured ACK/NACKcodebook, based on the ACK/NACK feedback data.

At the BS 170, a baseband received signal, y_(j), demodulated from theACK/NACK RF signal 432 in a time slot with index j may be represented asfollows:

y _(j) =h _(j)α_(j) s+n _(j)

where: h_(j) is representative of an aggregate channel vector from theBS 170 to the UE 110 and back to the BS 170; α_(j) is representative ofthe j^(th) ACK/NACK codeword vector selected from the pre-configuredACK/NACK codebook; s is representative of the DL symbol transmitted, bythe BS 170, in the TB 412; and n_(j) is a noise vector.

Since the symbol s is representative of the DL symbol transmitted by theBS 170, the BS 170 already knows s. However, from the received signal,y_(j), it is the task of the BS 170 to estimate both α_(j) and h_(j).The problem of estimating both vectors from the received signal may beconsidered challenging.

One solution to this estimation problem begins with receipt, at the BS170, of the mirror RF signal 430. The mirror RF signal 430 does notinclude an ACK/NACK codeword vector. Accordingly, the BS 170 can analyzethe baseband component, y₁, of the mirror RF signal 430 to estimate onlythe aggregate channel vector, h₁. Rather than considering that theACK/NACK codeword vector is absent from the received signal, it may beconsidered that the ACK/NACK codeword vector, α₁, is all ones.

It is then assumed that the aggregate channel does not change much fromthe first time slot 402-1 to the second time slot 402-2. Accordingly,the BS 170 can simplify the analysis of the baseband component, y₂, ofthe first ACK/NACK RF signal 432-1 to estimate the ACK/NACK codewordvector, α₂, by substituting the known aggregate channel vector, h₁, forthe unknown aggregate channel vector, h₂. Once the ACK/NACK codewordvector, α₂, has been estimated, the BS 170 may, again, perform ananalysis of the baseband component, y₂, this time with the ACK/NACKcodeword vector, α₂, known and the result being an estimate for theunknown aggregate channel vector, h₂.

More generally, the BS 170 can simplify the analysis of the basebandcomponent, y_(j+1), of the (j+1)^(th) ACK/NACK RF signal 432-(j+1) toestimate the ACK/NACK codeword vector, α_(j+1), by substituting theknown aggregate channel vector, h_(j), for the unknown aggregate channelvector, h_(j+1). Once the ACK/NACK codeword vector, α_(j+1), has beenestimated, the BS 170 may, again, perform an analysis of the basebandcomponent, y_(j+1), this time with the ACK/NACK codeword vector,α_(j+1), known and the result being an estimate for the unknownaggregate channel vector, h_(j+1).

Design of the pre-configured ACK/NACK codebook relates to a manner ofmapping ACK/NACK feedback data to an ACK/NACK codeword vector. Asdiscussed hereinbefore, the ACK/NACK codeword vector is used, by thepassive device components 210 of the UE 110, to alter a given RF signalwhile reflecting the given RF signal.

A given ACK/NACK codeword vector, α, may be expanded to illustrate thatthe ACK/NACK codeword vector, α, includes n elements. That is, α=(α₁,α₂, . . . , α_(n)), where each of the elements α_(i) is a complexsymbol. In step 514, the passive device components 210 reflect thesecond RF signal 412-2 as the first ACK/NACK RF signal 432-1 by alteringthe second RF signal 412-2. It may be understood that a given time slot402 may be subdivided into n sub-slots. Then, in the context of theACK/NACK codeword vector, α, including n ACK/NACK elements, reflectingthe second RF signal 412-2 as the first ACK/NACK RF signal 432-1 mayinvolve multiplying the second RF signal 412-2 by a respective one ofthe n ACK/NACK elements in each sub-slot among the n sub-slots.

The pre-configured ACK/NACK codebook, A, may be understood to include MACK/NACK codeword vectors, A=[α₁, α₂, . . . , α_(M)]. The size, M, ofthe preconfigured ACK/NACK codebook reflects a quantity of informationthat may be transmitted by the UE 110 in the form of the ACK/NACK RFsignal 432. The quantity, m, of ACK/NACK information bits may beconsidered to be related to the quantity, M, of ACK/NACK codewordvectors by the relationship m=log₂ M.

In a single-UE scenario, it is assumed herein that singular ACK/NACKfeedback data is transmitted in each ACK/NACK RF signal 432, i.e., eachACK/NACK RF signal 432 is considered to relate to a single receiveddecoded TB 422. To help the receiver 354 distinguish between the mirrorRF signal 430 (no ACK/NACK data) and the first ACK/NACK RF signal 432-1(with ACK/NACK data), a constraint of α₁≠1 may be imposed on theACK/NACK codeword vectors, meaning that the first element of allACK/NACK codeword vectors should not be equal to 1. Also, for definingthe ACK/NACK codeword vector mapping, the NACK for the (t−l)^(th)decoded TB 422-(t−1) may be defined, where l can be greater than 1(unlike the conventional ACK/NACK, where only the previous decoded TB istargeted for NACK reporting). For example, we can define the followingmapping:

ACK for TB(t−1)→α₁, NACK for TB(t−1)→α₂, NACK for TB(t−2)→α₃, etc. It ispossible that the UE 110 sends a NACK for a previous decoded TB 422 butthe BS 170 interprets the NACK as an ACK and sends a new TB 412. In thiscase, the UE 110 sends a NACK for TB(t−2) and, thereby, asks forretransmission of TB(t−2). Accordingly, more protection for ACK/NACK isprovided due to the passive nature of these communications. In addition,the NACK may also contain a revision number for retransmission.

Another criteria for defining the codebook, A=[α₁, . . . , α_(M)], is todesign the codebook in an asymmetric way in terms of error probability.Such a design criterion provides additional protection againstinterpreting a NACK as an ACK and, thereby, missing a packet. In otherwords, assuming that ACK is mapped to codeword vector α₁, the minimumdistance between codeword vector α₁ and the rest of the codeword vectorsin the codebook should be kept large to minimize the probability of p(α₁detected|α_(m) transmitted).

One advantage of aspects of present application is that multiple UEs 110may send ACK/NACK RF signals 432 to the BS 170 simultaneously regardingthe simultaneous DL transmission to those UEs 110. Beneficially, sincethe BS 170 transmits scheduled transmission to multiple UEs 110, the BS170 already knows which of the UEs 110 have potential to feedbackACK/NACK data to the BS 170. Accordingly, the problem of detecting theUE 110 at the origin of an ACK/NACK RF signal 432 is simpler than thesame problem in a grant-free scenario, in which the BS 170 has no apriori information regarding which UEs 110 are active. One challengepresent in the multi-UE scenario is related to defining the ACK/NACKcodebooks to better decode ACK/NACK RF signals 432 received, at the BS170, from multiple UEs 110.

According to aspects of the present application, UE-specific ACK/NACKcodebooks may be defined. That is, the ACK/NACK codebook defined for thefirst UE 110-1 is different from the ACK/NACK codebook defined for thesecond UE 110-2.

In a first approach to UE-specific ACK/NACK codebook design, a basecodebook is designed initially. An identifier, a “UEID,” may beassociated with each UE 110. To define the ACK/NACK codebook for thej^(th) UE 110-j some function of the UEID associated with the j^(th) UE110-j may be applied to the base codebook. Example functions that may beapplied to the base codebook may include a unitary transformationfunction and a scrambling function, inter alia.

In a second approach to UE-specific ACK/NACK codebook design, a supercodebook is defined initially. The super codebook may, for example,contain at least M×N unique codeword vectors, so that each UE 110 amongN UEs 110 may be assigned a codebook that is defined to include Mcodeword vectors selected from among the M×N unique codeword vectors.

According to aspects of the present application, the number, N, is fixedand is representative of the number of UEs 110 that have the potentialto perform passive RF signal reflection with included ACK/NACK data.According to other aspects of the present application, the number, N, isrepresentative of a number of UEs 110 currently performing passiveACK/NACK transmission in a given network.

Notably, the UE 110 carries out passive RF signal reflection withincluded ACK/NACK data in view of a plurality of configurationparameters. In addition to the codebook discussed hereinbefore, otherconfiguration parameters include ACK/NACK RF signal time slot duration,complex symbol duration and number of complex symbols per time slot.

Up to this point, aspects of the present application have been describedin the context of receipt, at the UE 110, of DL transmissions from theBS 170. It will be appreciated by those of skill in the art that aspectsof the present application may be useful in the context of receipt, atthe UE 110, of sidelink (SL) transmissions from another UE 110.Additionally, aspects of the present application may be useful in thecontext of receipt, at the BS 170, of uplink (UL) transmissions from theUE 110. In both alternative cases, it is understood that the UE 110 thatis at the origin of either the SL transmissions or the SL transmissionsis capable of full-duplex communication.

It should be appreciated that one or more steps of the embodimentmethods provided herein may be performed by corresponding units ormodules. For example, data may be transmitted by a transmitting unit ora transmitting module. Data may be received by a receiving unit or areceiving module. Data may be processed by a processing unit or aprocessing module. The respective units/modules may be hardware,software, or a combination thereof. For instance, one or more of theunits/modules may be an integrated circuit, such as field programmablegate arrays (FPGAs) or application-specific integrated circuits (ASICs).It will be appreciated that where the modules are software, they may beretrieved by a processor, in whole or part as needed, individually ortogether for processing, in single or multiple instances as required,and that the modules themselves may include instructions for furtherdeployment and instantiation.

Although a combination of features is shown in the illustratedembodiments, not all of them need to be combined to realize the benefitsof various embodiments of this disclosure. In other words, a system ormethod designed according to an embodiment of this disclosure will notnecessarily include all of the features shown in any one of the Figuresor all of the portions schematically shown in the Figures. Moreover,selected features of one example embodiment may be combined withselected features of other example embodiments.

Although this disclosure has been described with reference toillustrative embodiments, this description is not intended to beconstrued in a limiting sense. Various modifications and combinations ofthe illustrative embodiments, as well as other embodiments of thedisclosure, will be apparent to persons skilled in the art uponreference to the description. It is therefore intended that the appendedclaims encompass any such modifications or embodiments.

What is claimed is:
 1. A method for an apparatus to reduceacknowledgement (ACK) or negative acknowledgement (NACK) transmissionlatency, the method comprising: receiving, by the apparatus, a firstradio frequency (RF) signal comprising a first transport block;attempting, by the apparatus, to demodulate and decode the firsttransport block from the first RF signal; receiving, by the apparatus, asecond RF signal after the first RF signal; and reflecting, by theapparatus, the second RF signal while altering the second RF signal, thealtered and reflected second RF signal comprising a first feedbackindicative of whether the first transport block was correctly orincorrectly demodulated and decoded by the apparatus.
 2. The method ofclaim 1, wherein the first feedback is a first ACK/NACK codeword vectorcomprising a plurality of complex symbols.
 3. The method of claim 2,further comprising selecting, by the apparatus, the first ACK/NACKcodeword vector from a codebook comprising a plurality of ACK/NACKcodeword vectors.
 4. The method of claim 3, wherein the codebook isdevice-specific to the apparatus and the method further comprises:receiving, by the apparatus, a base codebook; and applying a function ofan identifier of the apparatus to the base codebook to generate thedevice-specific codebook.
 5. The method of claim 3, wherein the codebookis device-specific to the apparatus and the method further comprisesreceiving the device-specific codebook, where the device-specificcodebook forms part of a super codebook that includes a plurality ofcodebooks.
 6. An apparatus comprising: a memory storingcomputer-executable instructions; a processor adapted, by executing thecomputer-executable instructions, to: receive a first radio frequency(RF) signal including a first transport block; attempting, by theapparatus, to demodulate and decode the first transport block from thefirst RF signal; receive a second RF signal after the first RF signal;and reflect the second RF signal while altering the second RF signal,the altered and reflected second RF signal including a first feedbackindicative of whether the first transport block was correctly orincorrectly demodulated and decoded by the apparatus.
 7. The apparatusof claim 6, wherein the first feedback is a first ACK/NACK codewordvector comprising a plurality of complex symbols.
 8. The apparatus ofclaim 6, wherein the processor is further adapted, by executing thecomputer-executable instructions, to select the first ACK/NACK codewordvector from a codebook comprising a plurality of ACK/NACK codewordvectors.
 9. The apparatus of claim 6, wherein the codebook isdevice-specific to the apparatus and the processor is further adapted,by executing the computer-executable instructions, to: receive a basecodebook; and apply a function of an identifier of the apparatus to thebase codebook to generate the device-specific codebook.
 10. Theapparatus of claim 6, wherein the codebook is device-specific to theapparatus and wherein the processor is further adapted, by executing thecomputer-executable instructions, to receive the device-specificcodebook, where the device-specific codebook forms part of a supercodebook that includes a plurality of codebooks.
 11. A method, at anapparatus, of receiving acknowledgement (ACK) or negativeacknowledgement (NACK) transmissions, the method comprising:transmitting, by the apparatus, a first radio frequency (RF) signalcomprising a first transport block; transmitting, by the apparatus, asecond RF signal after the first RF signal; and receiving, by theapparatus, an altered and reflected version of the second RF signalincluding a first feedback indicative of whether the first transportblock was correctly or incorrectly demodulated and decoded.
 12. Themethod of claim 11, wherein the first feedback is a first ACK/NACKcodeword vector comprising a plurality of complex symbols.
 13. Themethod of claim 12, further comprising transmitting, by the apparatusand before the transmitting the first RF signal, a codebook including aplurality of ACK/NACK codeword vectors.
 14. The method of claim 13,wherein the plurality of ACK/NACK codeword vectors includes the firstACK/NACK codeword vector.
 15. The method of claim 13, wherein thecodebook is a base codebook that may be adapted to be a device-specificcodebook including the first ACK/NACK codeword vector.
 16. The method ofclaim 11, wherein the first feedback includes an indication that thefirst transport block was incorrectly demodulated and decoded, themethod further comprising transmitting, by the apparatus, a third RFsignal comprising the first transport block.
 17. An apparatuscomprising: a memory storing computer-executable instructions; aprocessor adapted, by executing the computer-executable instructions,to: transmit a first radio frequency (RF) signal comprising a firsttransport block; transmit a second RF signal after the first RF signal;and receive an altered and reflected version of the second RF signalincluding a first feedback indicative of whether the first transportblock was correctly or incorrectly demodulated and decoded.
 18. Theapparatus of claim 17, wherein the first feedback is a first ACK/NACKcodeword vector comprising a plurality of complex symbols.
 19. Theapparatus of claim 18, wherein the processor is further adapted, byexecuting the computer-executable instructions, to transmit, before thetransmitting the first RF signal, a codebook including a plurality ofACK/NACK codeword vectors.
 20. The apparatus of claim 19, wherein theplurality of ACK/NACK codeword vectors includes the first ACK/NACKcodeword vector.
 21. The apparatus of claim 19, wherein the codebook isa base codebook that may be adapted to be a device-specific codebookincluding the first ACK/NACK codeword vector.
 22. The apparatus of claim17, wherein the first feedback includes an indication that the firsttransport block was incorrectly demodulated and decoded, the processoris further adapted, by executing the computer-executable instructions,to transmit a third RF signal comprising the first transport block.